Diamond surface conductivity after exposure to molecular hydrogen

We report experimental evidence of a substantial reduction of the sheet resistance of a commercially available (110) oriented natural diamond surface after exposure not to atomic but to molecular hydrogen. In a conventional CVD reactor, we have merely exposed the sample to high purity molecular hydrogen fluxes at 800 °C. After exposure to air, the surface conductivity increased several orders of magnitude as measured by a professional collinear four-point probe head with tungsten carbide tips. After annealing at 900 °C in vacuum (P < 10^? 5 Pa) the conductivity dropped at least 4 orders of magnitude; repeatability tests on the measurements of the surface conductivity after thermal hydrogenation and subsequent air exposure were conducted in order to avoid systematic errors. Similar experiments were conducted at different process temperatures in order to evaluate the best process conditions. Thermal hydrogenation appears to be ineffective at increasing the surface conductivity of (100) homoepitaxial CVD diamonds.